linux-kernel - Re: [PATCH 1/2] irq/irq_sim: provide irq_sim_fire

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Message-ID: <20181125211854.idnqxz4pco3r7ydr@pengutronix.de>
Date:   Sun, 25 Nov 2018 22:18:54 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH 1/2] irq/irq_sim: provide irq_sim_fire_edge()

On Fri, Nov 23, 2018 at 04:59:46PM +0100, Bartosz Golaszewski wrote:
> śr., 21 lis 2018 o 20:15 Uwe Kleine-König
> <u.kleine-koenig@...gutronix.de> napisał(a):
> >
> > Hello Bartosz,
> >
> > On Wed, Nov 21, 2018 at 05:34:32PM +0100, Bartosz Golaszewski wrote:
> > > wt., 20 lis 2018 o 18:17 Uwe Kleine-König
> > > <u.kleine-koenig@...gutronix.de> napisał(a):
> > > >
> > > > On Tue, Nov 20, 2018 at 02:40:31PM +0100, Bartosz Golaszewski wrote:
> > > > > From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> > > > >
> > > > > The irq_sim irqchip doesn't allow to configure the sensitivity so every
> > > > > call to irq_sim_fire() fires a dummy interrupt. This used to not matter
> > > > > for gpio-mockup (one of the irq_sim users) until commit fa38869b0161
> > > > > ("gpiolib: Don't support irq sharing for userspace") which made it
> > > > > impossible for gpio-mockup to ignore certain events (e.g. only receive
> > > > > notifications about rising edge events).
> > > > >
> > > > > Introduce a specialized variant of irq_sim_fire() which takes another
> > > > > argument called edge. allowing to specify the trigger type for the
> > > > > dummy interrupt.
> > > >
> > > > I wonder if it's worth the effort to fix irq_sim. If you take a look in
> > > > my gpio-simulator patch, it is trivial to get it right without external
> > > > help with an amount of code that is usual for a driver that handles
> > > > irqs.
> > >
> > > You're basically recommending handcrafting another local piece of code
> > > for simulating interrupts - something that multiple users may be
> > > interested in. You did that in your proposed gpio-simulator and I
> > > still can't understand why you couldn't reuse the existing solution.
> > > Even if it's broken for your use-case, it's surely easier to fix it
> > > than to rewrite and duplicate it? There are very few cases where code
> > > consolidation is not a good thing and I don't think this is one of
> > > them.
> >
> > I don't say that factoring out common stuff is bad. But if in the end
> > you call
> >
> >         irq_sim_something(some, parameters, offset);
> >
> > with the simulator and if you don't use the irq simulator you do
> >
> >         irq = irq_find_mapping(irqdomain, offset);
> >         generic_handle_irq(irq);
> >
> > I prefer the latter because it's only a single additional line and in
> > return it's more obvious what it does because it's the same that many
> > other drivers (for real hardware) also do.
> 
> I'm not sure I'm following you. You still need to add ~150 LOC for the
> gpio_simulator_irqtrigger() worker and gpio_simulator_irq_*() routines
> locally as you did in your gpio-simulator patch. A generic simulator +
> using the irq_work saves you that.

If you teach the irq-sim driver everything that the gpio-simulator does
in the functions you pointed out then this is for sure functionality
that other users of the irq-sim code won't make use of. This is about
tracking the level of the gpio/irq line and the interrupt enable and raw
status bits that usually happen in hardware. The dummy iio driver won't
need that for sure as it only cares about triggering an irq and doesn't
even specify an irq type.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |